Reentry vehicles, missiles and other aerodynamic bodies are subjected to various instabilities in their flight dynamics. These effects may degrade flight performance and negate desired flight objectives. The effects may subject the vehicle to excessive or insufficient centrifugal or centripetal forces. Also, these effects may adversely modify the angle of attack of the body.
Unwanted modifications of flight dynamics may result from improper roll rate. Improper roll rate is a function of aerodynamic asymmetries that may result from insufficient manufacturing tolerances. These asymmetries may be difficult to engineer out of the system. Furthermore, any such engineering may increase the manufacturing cost of the vehicle. Therefore, it is useful to control roll rate by employment of a roll rate controller rather than imposing excessive tolerance standards on the vehicle. It is desirable to maintain a relatively constant roll rate to simplify the guidance and pitch control components of the vehicle. Absent roll rate control, the roll rate is proportional to the velocity. Velocity and consequently roll rate may vary by a factor of about 3 through the vehicle flight. Also, the roll rate may be highly responsive to the geometric requirements of the vehicle, such as wrap around tail fins. Therefore, roll rate is a highly variable characteristic and a stabilizer system is preferred to exacting extremely close tolerances. In some designs, the requirement of extremely close tolerances is still inadequate to yield the desired roll rate characteristics during the flight. Some method of controlling the roll rate is required.
Control systems that have previously been employed include the type that utilize vehicle internally generated energy, sensing instrumentation and a control actuation system. The deficiency in these systems are the addition of excessive weight to the vehicle and the power drain on the vehicle energy system.
They are also cumbersome and occupy an excessive part of the vehicle volume. Other systems are known as passive in that they utilize body geometry and aerodynamic effects to control the roll rate. These systems have been lacking in reliability and are not extensively employed. Furthermore, many of these devices are sensitive to vehicle maneuvering. The acceleration forces developed during such maneuvering adversely affect the stabilizing characteristics of these devices.
A roll rate control stabilization system has been needed that is actuated by and sensitive to the centrifugal and centripetal forces developed by the vehicle. The prior art is particularly deficient in providing a control system in which the roll rate imbalance is the motivating force in correcting the roll rate and which is compact, simple and insensitive to vehicle maneuvering.